The Java™ 2 Platform, Enterprise Edition (J2EE), from Sun Microsystems, Inc. of Palo Alto, Calif., defines a standard for developing multi-tier enterprise applications. A J2EE connector architecture is useful for the integration of J2EE-compliant application servers with at least one enterprise information system (EIS). There are typically two parts to this architecture: an EIS vendor-provided resource adapter and an application server to which the resource adapter plugs-in, such as a WebLogic Server available from BEA Systems in San Jose, Calif. This architecture defines a set of contracts that a resource adapter has to support to plug-in to an application server. These contracts can include such functions as transactions, security, and connection management. The J2EE connector architecture also defines a common client interface (CCI) that can be used to access an EIS. A CCI defines a client API for interacting with heterogeneous EIS systems, which enables application components and Enterprise Application Integration (EAI) frameworks to drive interactions across heterogeneous EIS systems using a common client API.
Containers
J2EE organizes business logic into reusable components. A J2EE server can provide underlying services for these components in the form of a container for every component type. Containers are the interface between the components and the platform-specific functionality that supports these components. Before a component can be executed, it is assembled into a J2EE application and deployed into the appropriate container.
Resource Adapters
A resource adapter is a system-level software driver used by an application server to connect to an EIS. A resource adapter, which can contain a library specific to an EIS, can serve as a J2EE connector. A J2EE connector architecture can support resource adapters that are developed by EIS developers, vendors, and/or third-party application developers. These resource adapters can be deployed in any application server supporting the appropriate J2EE specification. Resource adapters contain the Java, and if necessary, the native components required to interact with the EIS.
A J2EE connector architecture can provide packaging and deployment interfaces, so that various resources adapters can easily plug into compliant J2EE application servers in a modular manner. A J2EE connector architecture can be implemented in an application server and an EIS-specific resource adapter.
Architecture Components
A J2EE connector architecture typically has three main components:    (1) system-level contracts between the resource adapter and the application server, (2) a CCI that provides a client API for Java applications and development tools to access the resource adapter, and (3) packaging and deployment interfaces that provide the ability for various resource adapters to plug into J2EE applications in a modular manner.System Support
The J2EE connector architecture can provide a Java-based solution to the problem of connectivity between a multitude of application servers and EIS systems. By using the connector architecture, an EIS vendor does not need to customize a product for each application server. By conforming to the J2EE connector architecture, custom code is not required in order to extend support connectivity to a new EIS. The connector architecture enables an EIS vendor to provide a standard resource adapter for its EIS. This resource adapter plugs into an application, such as WebLogic Server, and provides the underlying infrastructure for the integration between an EIS and the application.
A resource adapter provider can develop a set of Java interfaces and classes as part of the adapter implementation. These Java classes implement J2EE Connector Architecture-specified contracts and EIS-specific functionality provided by the resource adapter. The Java interfaces and classes are then packaged together with a deployment descriptor to create a resource adapter module. This module can include any required native libraries, help files, documentation, and other resources. A deployment descriptor defines the contract between a resource adapter provider and a deployer for the deployment of a resource adapter.
J2EE connectors can be used to access legacy systems in accordance with J2EE guidelines. A J2EE connector can be used to access the legacy system in order to implement business logic. This business logic can be implemented either by using J2EE server-side components, such as may include an Enterprise JavaBean (EJB) or Java servlet, or by using J2EE client-side components, such as JavaRMI clients. Some examples of legacy systems include Oracle DB2 databases from Oracle Corporation of Redwood Shores, Calif.; IBM mainframe systems from International Business Machines Corporation of Armonk, N.Y.; Enterprise Resource Planning (ERP) systems such as SAP from SAP of Walldorf, Germany and PeopleSoft from PeopleSoft of Pleasanton, Calif.; and Customer Relation Management (CRM) solutions such as Siebel from Siebel Systems, Inc. of San Mateo, Calif. and Oracle's CRM solution from Oracle Corporation of Redwood Shores, Calif.
J2EE Components
A J2EE component itself is typically one of three types: (1) a code file, such as a Java class file; (2) a configuration file, such as an XML configuration file; or (3) a resource file, such as an image file, video file, or audio file that can be used by any appropriate Java classes.
Supporting Additional Systems
If it becomes necessary for an application to access a second legacy system, or another portion of the legacy system, it is necessary to create a second J2EE connector component using existing methods. This leads to not only the need for redundant coding, but also leads to the need to add any updates to both components as well as the need to allocate twice as much memory to store both components.